Fluorescent dyes have historically been used in a variety of commercial applications. Fluorescent dyes are commercially used as brighteners for white paper, laundry detergents and white polyvinyl chloride pipe. Fluorescent inks are often used as an "invisible ink" to facilitate cutting and sowing of fabric in the garment industry. Fluorescent dye has also been used to identify sources of water, oil and gasoline. The electronics industry has used fluorescent dye technology to automate and control inspection of thin coatings. Fluorescent tracers have also been used to ensure removal of corrosive fluxes arising from soldering and to locate glue smudges before staining wood furniture.
Fluorescent dyes have long been used as a nondestructive method of locating surface cracks in metals. To locate surface cracks, a solution containing a fluorescent dye is first applied to a metal surface. The fluorescence dye is then wiped from the metal surface leaving fluorescent dye in microcracks. An ultra violet light source is then used to locate microcracks by exciting the fluorescent dye within microcracks. The excited dye fluoresces to produce visible light within microcracks not visible by unaided eyesight.
Weldable materials such as filler metals and strip welded into tubing are highly sensitive to residues remaining from metal processing operations. The cleanliness requirements for good weldability are not visually determinable. An extremely small amount of lubricant left on a filler metal after a cleaning operation may cause a filler metal to lose its welding characteristics. Thus, cleaning operations for weldable materials are extremely important. An example of the importance of cleaning filler metal is illustrated in U.S. Pat. No. 4,763,677 which discloses a multistage ultrasonic cleaning device.
The present state of the art for monitoring cleanliness of filler metals has not changed in over forty years. There are essentially two methods of determining whether a filler metal is sufficiently clean for obtaining acceptable welding characteristics. The first method is to weld with a sample of the material to verify welding performance and use radiographic inspection or other methods to evaluate porosity. The second method is to remove a representative short section of filler metal and weigh the removed material as accurately as possible to provide an initial weight. Then the representative wire is treated with a strong base to remove any residue from the filler metal, dried and weighed to determine a final weight. The difference between initial and final weight is used to determine whether the amount of residue on the filler metal is acceptable.
Problems with state of the art monitoring of filler metal cleaning include inaccuracy and delay. Inaccuracy arises from measuring only a small portion (one meter) of a wire that may be a few kilometers long and from the relatively high level of error arising from measuring techniques. The delay problem arises from the fact that filler metals are typically not checked for impurities until after an entire spool of filler metal has been drawn. This delay in time, eliminates any chance of correcting a cleaning operation while filler metal is being processed.
It is an object of this invention to provide a method of increased accuracy for determining amount of treatment solution on the surface of weldable metal product.
It is a further object of this invention to provide a method of monitoring the entire length of a weldable metal product for treatment solution residue.
It is a further object of this invention to provide an immediate method of determining whether treatment solution residue is present.